The invention relates to a belt, strap, conveyor belt having at least one support fabric in which at least one electrically conductive loop is embedded. The invention relates also to a method of manufacturing such a belt, strap, conveyor belt.
Embedding continuous conductive loops in belts, straps, conveyor belts, et cetera for different monitoring purposes has been known for a long time. Conductive loops of this type are embedded particularly in continuous conveyor belts and the current flow generated in the conductive loops in an inductive manner is used to constantly monitor the moved conveyor belt and for example to recognize early damage, especially longitudinal tears, caused for example by foreign bodies penetrating. In the recent past it has also been proposed to allocate to each conductive loop in the conveyor belt a transponder, comprising an integrated circuit which is connected in a conductive manner to a coil. In this case, the conductive loops are supplied with energy in an inductive manner by a device situated outside the conveyor belt, which energy they, in turn, couple in an inductive manner to the transponders allocated to them. In the reverse direction, the transponders transmit an individual identifier stored in their circuits to the device. From the reception of the signal, the external device assesses the soundness of the conductive loop or of the transponder and thus the soundness of the conveyor belt in the region of the conductive loop. Conversely, if the individual identifier is not transmitted, it is concluded that there is damage of the conductive loop and thus damage of the conveyor belt in the region of the conductive loop (see also DE 44 44 262 where a monitoring system of this type is described in detail).
The above remarks show that reliable monitoring with the aid of conductive loops is only possible if the failure of a conductive loop can only be traced back to damage of the belt, strap, conveyor belt etc. Thus special importance attaches to the resistance of the conductive loops to everyday loads. In addition, conductive loops for monitoring purposes are also intended to be embedded in particularly thin conveyor belts, which have as the strength support at least one support fabric in the form of a textile ply and are only covered by a very thin elastomer cover layer. It is obvious that the demands made of the conductive loop, namely high durability and the possibility of being embedded in conveyor belts having a support fabric and an extremely thin cover layer, are opposed to one another.
From DE 196 01 899 C1, it is known to produce the conductive loops from an electrically conductive foil and to embed them in a conveyor belt. The conductive loops have a thickness of between 20 xcexcm and 200 xcexcm, so that they are also suitable for embedding in conveyor belts having extremely thin cover layers. If the conveyor belt has steel cables as strength support, it has been shown that the conductive loops can also resist high mechanical everyday bending and tensile loads. However, if the conveyor belt has one or more support fabrics as strength support, it has been shown that the conductive loops can only resist normal everyday bending and tensile loads, but can tear with high tensile loads even though these do not yet lead to damage of the conveyor belt. This can probably be traced back to the fact that with high tensile loads there can be stretching of the support fabric and thus stretching of the conductive loops which can lead to splitting of the conductive loops.
The object underlying the invention is to create a belt, strap, conveyor belt, et cetera (especially having at least one support fabric as the strength support), which on the one hand has a thin cover layer and on the other hand can be reliably monitored by embedded conductive loops. The object underlying the invention is also to create a method of manufacturing such a belt, strap, conveyor belt etc.
According to the invention this object is accomplished in that at least a portion of the electrically conductive loop is sewn onto the support fabric.
According to another embodiment of invention the object is in addition accomplished in that first a commercially available support fabric, known per se, is produced, onto which subsequently the electrically conductive loops are sewn, and that the belt, strap, conveyor belt, et cetera is completed in a manner known per se using the support fabric prepared in this manner. If the support fabric is to be embedded in a two-ply belt, it is preferably gummed onto the support fabric before the conductive loop is sewn on. If, however, the support fabric is to be embedded in a one-ply belt, it is preferably saturated with a PVC paste before the conductive loop is sewn onto the support fabric.
According to a further embodiment of the invention the object is accomplished in addition in that first a support fabric is produced which contains electrically conductive threads at a spacing from one another, of which subsequently respectively two are connected to form an electrically conductive loop by sewing on an electrically conductive seam, and in that the belt, strap, conveyor belt, et cetera is completed in a manner known per se using the support fabric prepared in this manner. Before the electrically conductive seams are sewn on, the support fabric can be treated as per the previous paragraph.
According to another embodiment of the invention the object is accomplished in addition in that first the loop 4 is sewn onto a grid-like support fabric, and in that the support fabric prepared in this manner is introduced into the conveyor belt blank at any position, and the conveyor belt is completed in a manner known per se.
The basic idea of the invention can be seen in the fact that the conductive loops consist of threads which are sewn directly onto the support fabric like a seam, or which are already contained in the support fabric. The conductive loops thus consist of a material which has very similar or identical deformation properties to the threads of the support fabric.
The advantages of the invention can be seen in particular in the fact that even belts, straps, conveyor belts, et cetera, which have at least one support fabric as strength support and an extremely thin cover layer, can be provided with conductive loops. It has been shown that even conveyor belts, which have a cover layer with a thickness ofxe2x89xa66 mm, can be provided with conductive loops. Nevertheless the conductive loops embedded in the conveyor belt resist high mechanical loads, in particular tensile loads. This can be traced back to the fact that the conductive loops consisting of threads have (practically) the same deformation properties as the threads of the support fabric such that the stretching of the support fabric is transferred to the conductive loops.
The advantages of the manufacturing method according to the invention can be seen in particular in the fact that, through the production of a commercially available support fabric in a first method step, a high flexibility in the manufacture of the conveyor belts is achieved. Thus, the commercially available support fabric can be intermediately stored and it is possible to react flexibly to customers"" wishes with respect to equipping conveyor belts with conductive loops, since the conductive loops are sewn only subsequently onto the support fabric.
The advantages of the method according to the further embodiment can be seen in particular in the fact that components of the conductive loops are incorporated in the support fabric already during the manufacture of the support fabric. The electrically conductive threads which are present in the support fabric merely have to be subsequently connected to one another to be conductive, so that the complexity for subsequent sewing is reduced.
The advantages of the method according to the further embodiment can be seen in particular in the fact that through the method, even belts, straps, conveyor belts etc. with a metallic tension carrier can be provided with conductive loops in a simple manner.
According to a first embodiment of the invention, the support fabric contains electrically conductive threads which run largely in the transverse direction of the support fabric, and of which respectively two are connected to one another by electrically conductive threads sewn onto the support fabric.
According to an alternative embodiment of the invention, the complete conductive loops are entirely sewn onto the support fabric of the conveyor belt. Here, a galvanized or coppered steel wire can be used as the thread which forms the electrically conductive loop in the seam. The use of a steel wire has the advantage of high strength and high flexibility, such that the conductive loop can particularly well xe2x80x9cgo along withxe2x80x9d stretching of the conveyor belt under tensile load and thus stretching of the support fabric. It has emerged that a galvanized steel wire has sufficient electrical conductivity. Particularly good electrical conductivity can, however, be achieved in that the steel wire is covered with a copper coating.
Alternatively, a copper wire can be used as the thread which forms the electrically conductive loop in the seam. The advantage of this development can be seen in the fact that a copper wire has optimum conductivity. Independently of the material of which the thread consists, which forms the electrically conductive loop in the seam, the other threads used in sewing on the conductive loop do not have to consist of an electrically conductive material. Rather, polyester threads can be used, for example, as additional threads.
According to a development of the invention, the thread which forms the conductive loop in the seam has a plurality of fibrils, preferably 3 to 20 fibrils, and thus particularly high flexibility. The advantage of this development can be seen in the fact that conductive loops formed from threads of this kind can absorb particularly high mechanical tensile loads. If a thread with a plurality of fibrils is used, some fibrils are preferably formed from copper and the remaining fibrils of the thread from steel, such that, on the one hand, there is good electrical conductivity (as a result of the copper portion) and, on the other hand, there is good strength and flexibility (as a result of the steel portion) of the thread.
According to a further development of the invention, the threads used to form the conductive loop have a diameter of between 0.1 and 1 mm. The advantage of this development can be seen in the fact that threads having such a diameter can be handled by commercially available sewing machines without any problems.
According to a further development of the invention, the two ends of a conductive loop sewn onto the support fabric are connected to one another by a covering seam which is led, starting from one end of the conductive loop, in a zigzag line or in a line similar to a zigzag line over the other end of the conductive loop. Through such a covering seam it can be guaranteed in a simple manner that the two ends of the conductive loop are electrically conductively connected to one another.
According to a further development of the invention, the conductive loops have a spiraled portion. The advantage of this development can be seen in the fact that the conductive loops can even better absorb length alterations of the support fabric without being destroyed. To achieve this advantage, when the conductive loop is sewn onto the support fabric, sewing methods are used in which spiraling of the thread is produced automatically by the guiding of the thread.
According to a further development of the invention, each conductive loop embedded in the belt, strap, conveyor belt etc. is operationally connected to an associated transponder, such that a monitoring system can be operated such as is described in detail, for example, in DE 44 44 262.